The invention relates to a method for preparing a charging plan for excavation of a rock cavern, the method comprising determining in advance at least drill hole locations in a pre-determined coordinate system for a round to be drilled into the rock cavern and creating a charging plan for the holes in the round by means of a computer-aided design program for blasting the round.
The invention further relates to an arrangement for designing a charging plan for excavating a rock cavern with a rock drilling apparatus comprising one or more drilling booms having a rock drilling unit attached to it and a control unit for controlling the drilling comprising a computer, whereby at least locations of drill holes in a predetermined coordinate system has been defined in advance for a round to be drilled which arrangement comprises a computer with the computer assisted design program for designing the charging plan.
Tunnels, underground storage silos and other rock caverns are excavated in rounds. In a tunnel or other part of a rock cavern, drill holes are drilled, and then charged and blasted after the drilling. One blast detaches from the rock an amount of rock material that equals that of one round. For excavating a rock cavern, a plan is made in advance and information about the rock type, for example, is determined. In general, the orderer of the rock cavern also sets various quality requirements for the cavern to be excavated.
When tunnel drilling is performed by a rock drilling apparatus provided with instrumentation, there is generally designed, as office work, a drilling plan for drilling a round and a charging plan for blasting the round. The drilling plan and the charging plan are supplied to the rock drilling apparatus for being used by means of its control computer. The drilling plan serves as a controlled instruction for drilling drill holes in the rock in such a manner that a desired round can be formed.
The successfulness of drilling and charging is measured, inter alia, by pull-out per round, which refers to the ratio of advance of the tunnel after a blast to a designed length in the drilling plan. Improvement of pull-out from 88 to 95 percent, for instance, means significant cost savings in an excavation project. In practice, defining an optimal pull-out is aimed at by changing the drilling plan or the charging plan. Examples of parameters applied in changing the charging plan include distances between the drill holes, specific charge, charging degree, blast cut in different areas of the plan.
For designing a charging plan there are developed design programs that assist the designer in composing the charging plan. Designing a charging plan is thus an interactive action between the designer and the design program.
Production of drilling plans and continuous design, as well as review of plans during tunnel work, have been developed in various ways in view of blasting techniques, for instance. This is presented in publication WO 2008/078001, for instance.
In practice, in round blasting it has been found that even though the hole locations and the size and amount of blasting charges are dimensioned as well as possible on the basis of the known facts, the outcome of the blast does not, however, meet the planned design. Typically, when detached material is removed after the blast, it may be found that the remaining rock surface deviates significantly from the theoretical surface that should have been created after the blast. This may result from a plurality of different factors, such as fracturing properties or hardness of rock, or some other factor that cannot have been known in advance with a sufficient accuracy. As a consequence, however, the efficiency of excavation deteriorates and this, in turn, causes quite significant additional costs.